ZDV is currently recommended for the treatment of HIV infected, symptomatic, pregnant women and asymptomatic pregnant women with CD4 lymphocyte counts between 200 and 500. With increasing numbers of women taking long term - as well as short term - ZDV treatment, it is important to explore the development of ZDV-resistant variants of HIV, as well as their potential for perinatal transmission. There is little data available to document the frequency of ZDV resistance among HIV-infected women and their subsequently infected infants. Understanding the frequency, effects and method of transmission for ZDV resistant HIV strains may influence future treatment choices for women and their infants. Phenotypic and genotypic assays for ZDV resistance will be performed on maternal as well as infant blood.